That makes more sense, and puts you in a better position for suitable fish. A GH of 151 ppm [mg/l is equivalent to ppm] which equates to 8 dGH (for those of us who prefer the smaller numbers!) is on the borderline of soft/medium hard. A pH below 7 is further indication of softer rather than harder so you should look at most of the South American and SE Asian species as far as water parameters are concerned; most will have no issues here. Which opens up a lot of options with a 30g long tank. I assume this length is 3 feet (90 cm)?